Mid-Wave Infrared Photoconductors Based on Black Phosphorus-Arsenic Alloys

Black phosphorus (b-P) and more recently black phosphorus-arsenic alloys (b-PAs) are candidate 2D materials for the detection of mid-wave and potentially long-wave infrared radiation. However, studies to date have utilized laser-based measurements to extract device performance and the responsivity of these detectors. As such, their performance under thermal radiation and spectral response has not been fully characterized. Here, we perform a systematic investigation of gated-photoconductors based on b-PAs alloys as a function of thickness over the composition range of 0-91% As. Infrared transmission and reflection measurements are performed to determine the bandgap of the various compositions. The spectrally resolved photoresponse for various compositions in this material system is investigated to confirm absorption measurements, and we find that the cutoff wavelength can be tuned from 3.9 to 4.6 μm over the studied compositional range. In addition, we investigated the temperature-dependent photoresponse and performed calibrated responsivity measurements using blackbody flood illumination. Notably, we find that the specific detectivity (D*) can be optimized by adjusting the thickness of the b-P/b-PAs layer to maximize absorption and minimize dark current. We obtain a peak D* of 6 × 10¹⁰ cm Hz^1/2 W^-1 and 2.4 × 10¹⁰ cm Hz^1/2 W^-1 for pure b-P and b-PAs (91% As), respectively, at room temperature, which is an order of magnitude higher than commercially available mid-wave infrared detectors operating at room temperature.